On The Suitability of Data From The Climatic Research Unit (CRU) and 5th Generation of European Reanalisis (ERA5) For Monitoring Drought Events Under a Probabilistic Framework

Abstract

The aim of this study was to evaluate the suitability of the Climatic Research Unit (CRU) and the 5th Generation of European ReAnalysis (ERA5) for calculating both SPI and SPEI and, hence, for drought monitoring in the state of São Paulo. Monthly precipitation (P) and air temperature data were used to calculate the SPI and the SPEI at time scales of 1, 6 and 12 months. Goodness-of-fit tests and indices of agreement were used in this study. It was observed low agreement between data provided by the CRU (P and P-ETP) and data from the surface stations. However, the SPI and SPEI estimates presented a slightly higher agreement, especially in the winter months at the monthly time scale. Equivalent results were found for the ERA5 data. A case study on the water crisis of 2014 showed that the drought indices calculated from the CRU data underestimated the drought episode. On the other hand, the indices calculated from ERA5 data overestimated the drought. Therefore, we concluded that the reanalysis data cannot be directly used for drought monitoring in the state of São Paulo.